Intensifier Pump Monitoring System

ABSTRACT

An apparatus and method of graphically indicating the performance of intensifier pumps used in water-jet cutting utilizes output signals from end-of-stroke proximity sensors to establish stroke times for the pump&#39;s plungers. The stroke times are then used to present bar graphs for each plunger reflecting the magnitude of the time valve by the height of the bars and performance status by the color of the bars.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates generally to water-jet cutting systems, and more particularly to a method and apparatus for monitoring the performance of intensifier pumps commonly employed in such water-jet cutting systems.

II. Discussion of the Prior Art

As is now well-known in the art, a water-jet cutter comprises a tool capable of slicing through a variety of materials using a jet of water at high velocity and pressure. Water-jet cutters are frequently used in the manufacture of machinery parts, fabrication of stone countertops and especially in applications where parts forming operations must be performed at lower temperatures than can be achieved using more conventional machining operations.

In water-jet cutters, a so-called intensifier pump or some other technology for creating high pressure is coupled to a cutting head having an outlet orifice less than one millimeter in diameter and the intensifier pump may deliver water at a pressure in a range from 10,000 to 100,000 psi and which when directed onto a work piece erodes through the material and is often guided by robotics such as a CNC machine.

To achieve these high pressures, a dual head reciprocating pump is typically driven by the output from a hydraulic pump. In this arrangement, hydraulic fluid is cyclicly applied to opposed sides of a relatively large diameter “piston” where the piston has attached to it first and second oppositely directed plungers of relatively smaller diameter and that fit within oppositely directed cylinders. In operation, during a pressure stroke in one cylinder, water is drawn through a low pressure poppet into the other cylinder during its suction stroke. Thus, as the hydraulic piston and plunger assembly reciprocates back and forth, it delivers high pressure water out of one side of the intensifier while low pressure water fills the opposite side.

Pressure multiplication is due to the difference in cross-sectional area between the piston on which the hydraulic fluid works and the area of the face of the plungers employed. Thus, if there is a 20-to-1 area difference, the hydraulic oil pressure acting on the piston is multiplied by a factor of 20.

It is known in the art to track the stroke time, i.e., the time to move from left-to-right or vice versa and to use that number to monitor for adverse conditions. An intensifier with a particular intensification ratio will stroke at a certain rate to achieve a particular output flow of water. This number is typically known through experimental or theoretical practice and is used for comparison to the actual stroke rate. When an intensifier strokes faster than the theoretical time, it can indicate any number of adverse conditions, including but not limited to, a high pressure leak, a blown orifice, bleed down valve failure, internal check valve leak or failure. It is also known in the art to use the stroke rate and comparison to calculate a theoretical value to trigger a warning or an alarm. Multiple thresholds of alarms can readily be set using basic calculations and comparisons. These alarm thresholds are discrete settings and provide limited, if any, early indication of impending system failure.

Accordingly, it is a principal object of the present invention to provide a monitoring system that yields a visual indication of actual intensifier performance for each and every stroke. In a healthy system, the intensifier will be stroking evenly from left-to-right and back again. In a multiple intensifier pump system, both intensifiers should be set to stroke at a similar rate to each other. The monitoring system with visual display of the present invention allows for quick and easy setup and balance of multiple systems.

SUMMARY OF THE INVENTION

A method and apparatus for displaying out-of-balance performance of an intensifier for water-jet cutting where the intensifier pump may comprise an inline configuration of a hydraulic cylinder containing a piston of a predetermined diameter and having first and second plungers affixed to opposed face surfaces of the piston and cylinder blocks affixed to opposed ends of the hydraulic cylinder and receiving the first and second plungers in cylinder bores formed in the cylinder blocks where the hydraulic cylinder is adapted to be coupled to a motor-driven hydraulic pump through a manifold that cyclicly delivers high pressure hydraulic fluid on the opposed face surfaces of the piston. The invention is characterized by having first and second end-of-stroke proximity sensors mounted on the cylinder blocks for producing electrical output signals. These electrical signals are fed to a microprocessor that is programmed to measure left-to-right and right-to-left cycle times for the first and second plungers. A graphics display panel is coupled to the microprocessor for graphically indicating when the stroke time values approach and exceed preset thresholds. More particularly, the graphics display presents side-by-side bars whose height and color reflect proper operation, limited but still acceptable operation, and an alarm or shutdown state of the intensifier pump assembly.

DESCRIPTION OF THE DRAWINGS

The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts.

FIG. 1 is a schematic illustration of an intensifier used in a water-jet cutter system incorporating features of the present invention;

FIG. 2 is a schematic block diagram of a computer and display forming part of the system of the present invention;

FIG. 3 is a software flow diagram showing the algorithm implemented in the microprocessor of FIG. 2; and

FIGS. 4A-4C are screen prints of the display panel for normal, conditional and alarm states for the pump, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT

This description of the preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as “lower”, “upper”, “horizontal”, “vertical”, “above”, “below”, “right”, “left”, “top” and “bottom” as well as derivatives thereof (e.g., “horizontally”, “downwardly”, “upwardly”, etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as “connected”, “connecting”, “attached”, “attaching”, “join” and “joining” are used interchangeably and refer to one structure or surface being secured to another structure or surface or integrally fabricated in one piece, unless expressively described otherwise.

Furthermore, and as used herein, the symbol SRL is an acronym for “Stroke Rate Left” which is the time between the occurrence of a right proximity sense pulse and a left proximity sense pulse. SRR is an acronym for “Stroke Rate Right” which is the time between the occurrence of a left proximity pulse and a right proximity pulse. The meaning of these terms will become clearer as the specification continues.

Referring first to FIG. 1, there illustrated a cross-sectional view through an intensifier of the type used in implementing water-jet cutters. The intensifier assembly is indicated generally by numeral 10 and is seen to comprise a hydraulic cylinder body 12 in which is reciprocally mounted a piston 14. Fitted between the peripheral surface of the piston 14 and the inner diameter of the hydraulic cylinder 12 is a piston seal 16 and a pair of wear rings 18.

Affixed with suitable seals to opposed ends of the hydraulic cylinder body 12 are a left cylinder end cap 20 and a right cylinder end cap 22. Mounted in each of the cylinder end caps 20 and 22 are proximity sensors 24 and 26 designed to produce an electrical output signal when the piston 14 reaches the end of its stroke and depresses either the left indicator pin 28 or the right indicator pin 30 against the force of return springs as at 32. In FIG. 1, the piston 14 is shown in its leftmost position and is displacing the indicator pin 28 to the left, moving a larger diameter portion thereof directly under the proximity sensor 24. Referring now to the right end cap 22, it can be seen that the return spring 32 is urging the indicator pin 30 to the left so that the enlarged portion of the indicator pin is no longer directly under the proximity sensor 26. Indicator pin caps 34 screw into the left and right hydraulic cylinder end caps 20 and 22 once the indicator pins and return springs have been inserted into the hydraulic end caps.

Affixed to the hydraulic cylinder end cap 20 is a left cylinder block 36. The cylinder block 36 contains a cylindrical bore 38 in which is fitted a spacer tube 40 that serves as a sleeve bearing for the left plunger 42.

In a similar fashion, there is attached to the right hydraulic end cap 22 a cylinder block 44 having a bore 46 containing a spacer tube 48 designed to reciprocally receive the right plunger 50 therein. The plungers 42 and 50 are supported within the left and right hydraulic cylinder end caps 20 and 22 by sleeve bearings 52 along with plunger seals 54. Housing seals as at 56 prevent leakage and cross-contamination of hydraulic fluid pumped into the hydraulic cylinder 12 and water drawn into a respective one of the bores 40 and 46 during its suction cycle.

Assembled onto the opposed ends of the cylinder blocks 36 and 44 are plunger end caps 58 and 60. Suitable O-rings seals are again provided to preclude fluid leakage through the joint between the cylinder blocks and their respective end caps.

Each of the end caps 58 and 60 includes a check valve body 62 that supports a low pressure poppet valve 64 and a high pressure poppet valve 66. The seat for the high pressure poppet valve is indicated by numeral 68.

The manner in which the plungers 42 and 50 are affixed to the piston 14 of the hydraulic cylinder 12 will now be explained. The inner ends of the plungers 42 and 50 have cylindrical collars 70 swaged thereon and fitted over these collars are plunger retainers 72 that are held in place by spring retainer rings, as at 74. In this fashion, the plungers 42 and 50 are captured on the piston 14 and are made to reciprocally move as hydraulic fluid from a source (not shown) is injected into the hydraulic cylinder on one side of the piston or the other.

The intensification or increase in pressure afforded by the intensifier 10 is due to the difference in area of the opposed faces of the piston 14 compared to the end face of the plungers 42 and 50. For example, with a piston of a diameter of 4.5 inches, it will have a cross-sectional area of 15.9 square inches. Assuming that the plungers 42 and 50 are of a 1 inch diameter, they would have an area of about 0.78 square inches. Thus, the area of the piston is almost 20 times that of the end face of the plungers. If it is assumed that the hydraulic oil is pressurized to, say, 3,000 psi, the pressure of water ejected through the high pressure outlet valves 66 will be about 60,000 psi.

In that the present invention is directed more to monitoring and displaying the performance of an intensifier pump assembly rather than the design of such pumps, it is deemed unnecessary to describe in detail the manner in which hydraulic oil under pressure is cyclicly applied to opposed side surfaces of the piston 14, all of which is well known to those skilled in the art. In known intensifier pump control, as the plungers reciprocate back and forth, end of travel sensing is usually achieved using proximity sensors, such as Hall effect devices, where the signal from such sensors is read into a processor and used to control the hydraulic valves for effecting reversal of the pump's stroke. It is also known in the art that by monitoring stroke time, i.e., time to move from left-to-right or vice versa, can be used to monitor for degradation in pump operating performance. An intensifier with a particular piston/plunger area ratio will stroke at a certain rate to achieve a particular water output flow. This factor is typically known through experimental or theoretical practice and is used for comparison to a pump's actual stroke rate. As mentioned earlier, when an intensifier strokes faster than the theoretical time, it can indicate any number of failing conditions.

The present invention provides an improved way of monitoring intensifier stroke rates and displaying the information to aid an operator in maintaining the system at an optimum condition. Details of this monitoring system will now be described.

Referring to FIG. 2, there is shown a simplified block diagram of the electronics for implementing the intensifier pump monitoring system. Signals from the left proximity sensor 24 and the right proximity sensor 26 are fed into a microprocessor-based controller 80 which is programmed to compute both SRL and SRR for each stroke of the pump 10 and to compare those stroke times with predetermined thresholds and to provide an output to a display panel 82.

A flow chart of the software program executed by the microprocessor-based controller is shown in FIG. 3 and with the pump 10 running when the left proximity sensor 24 produces an output it enables a gate in the microprocessor to pass timing pulses from the microprocessor's clock circuitry into a register initiating the start of a timer 84. When piston 74 reaches the indicator pin 30 for the right proximity sensor 26, it ends the timing period for the right stroke (SRR) and the contents of the timing register are stored as represented by block 86 in FIG. 3.

FIGS. 4A-4C comprise screen shots of the display panel 82 for several running conditions of the intensifier pump 10. Of interest are the vertical bars 88 and 90 which, by their height, are indicative of the instantaneous SRL and SRR values. Referring again to FIG. 3, a test is made at decision block 92 to determine whether the stored time value is less than a first threshold and if not, the bars are colored green as shown in FIG. 4A and as represented by operation blocks 94 and 96.

Had the test at decision block 92 reflected a change in the stroke time such that the stored time value became less than a first threshold, a further test is made at decision block 98 as to whether the stored time value is less than a second threshold lower than the first, and if not, the bars 88 and 90 are displayed in a second color, namely yellow, as shown in FIG. 4B, and as reflected in block 100 in the flow chart of FIG. 3. A yellow indication provides a warning that maintenance should be performed at the end of a job that is in progress. Had the stored time value become not only less than the first threshold but also less than a second threshold, the display would change the bars 88 and 90 representative of SRL and SRR to red as indicated by operation block 102. The second threshold is set to indicate a system failure condition and as a result, an alarm is sounded to alert the operator that the pump must be inspected and any failed parts replaced before cutting operations can continue. See block 104 in FIG. 3. It is to be understood that additional thresholds may be implemented in the software that would result in additional color indications when exceeded, not just green, amber and red.

As indicated earlier, the height level of the bars is reflected of the magnitude of the left and right stroke times SRL and SRR. Hence, in the flow diagram of FIG. 3, the stored stroke time values are used to indicate the color fill level that the selected color should reach in the bars 88 and 90. This is the operation reflected by block 106 in FIG. 3. After the completion of each SRR and SRL, control loops back over line 108 back to the left proximity sensor 24 initiating the next cycle of the pump.

It can be appreciated from the foregoing that the touch panel display 82 yields a visual indicator where a user receives accurate positive feedback of actual intensifier pump performance for each and every stroke. In a properly functioning system, the intensifiers typically will be stroking evenly from left-to-right and from right-to-left. The display is designed so that the bars 88 and 90 will fill to a higher level upon faster stroke. The actual stroke time is compared to a theoretical stroke time and then normalized to fill the bar graph. When the pump is stroking at an acceptable rate as reflected in FIG. 4B, the color of the bar graph may be green. When the pump strokes faster than the theoretical level, but slower than an alarm level set in the microprocessor program, the color of the bar graph turns yellow, as in FIG. 4B. Similarly, when the intensifier pump strokes faster than a set alarm level, the bar graph turns red as seen in FIG. 4C.

The display system of the present invention allows for the monitoring of two separate intensifiers of an intensifier pump system, as indicated by a second set of double bars in FIGS. 4A-4C. The four colored circles above the bars are indicative of the on/off state of a pair of intensifiers with green indicating the “on” state and red indicating the “off” state.

For purposes of explanation only, let it be assumed that the theoretical stroke time, both left and right, are equal to one second per stroke (TRL=TRR=1.0) and that the alarm stroke rate left and the alarm stroke rate right are both equal to 0.9 seconds per stroke (ARL=ARR=0.9). If SRL=0.95 seconds and SRR=0.98 seconds, then

X=TRL/SRL=1.0/0.95=1.05

Y=TRR/SRR=1.0/0.98=1.02.

For the above example, the bar graph would show a fill up to 105% for the left bar and 102% for the right bar and both fill colors would be yellow since X and Y both exceeds the theoretical limit that has been assumed. Also, the left bar is slightly higher than the right bar indicating a faster stroke.

If SRL had equaled 1.05 seconds and SRR had equaled 0.89 seconds, then:

X=1.0/1.05=0.95

Y=1.0/0.89=1.12.

In the latter example, the bar graph on the left would be as in FIG. 4A and only 95% filled and the color would be green indicating the stroke rate is slower than the predetermined theoretical rate. The right bar graph would show full and would be red because the 0.89 second stroke rate is faster than the alarm threshold which we assumed to be 0.90 seconds.

This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself. For example, rather than employing a bar graph, those skilled in the art will appreciate that a similar graphical presentation may be made on a circular pie chart or other mode of display that is capable of showing both magnitude and operational status, as is reflected by the bar charts of FIGS. 4A-4C. Also, while the intensifier shown in FIG. 1 is depicted as having a single piston supporting a pair of plungers, intensifiers have also been produced in which two hydraulic cylinders are arranged in tandem and where each includes a piston with only a single plunger affixed to and where each of the hydraulic cylinders has a single cylinder block that extend in opposite directions for receiving a plunger therein. The present invention can be adapted to this design as well by properly placing the proximity sensors to measure the stroke times for each plunger. 

What is claimed is:
 1. A method of displaying operational status of an intensifier for water-jet cutting systems comprising the steps of: (a) providing an intensifier having first and second cylinder blocks affixed to opposed ends of a hydraulic cylinder that contains a relatively large diameter piston to which is affixed at least one plunger of a lesser diameter than that of the piston slidably disposed in bores formed in the first and second cylinder blocks, the large diameter piston adapted to be driven in reciprocal strokes by pressurized hydraulic fluid injected into the hydraulic cylinder; (b) providing first and second proximity sensors for producing electrical signals upon the large diameter piston reaching an end of each stroke; (c) connecting a microprocessor to receive the electrical signals and programmed to compare the time required for the large diameter piston to move from right-to-left (SRL) with the time required to move from left-to-right (SRR); and (d) providing a display screen coupled to the microprocessor for graphically indicating when the stroke time drops below preset thresholds.
 2. The method as in claim 1 wherein the SRL is graphically represented by the size of a first image and SRR is represented by the size of a second image.
 3. The method of claim 2 wherein the first and second images comprise adjacently positioned bars whose length dimensions are proportional to SRR and SRL, respectively.
 4. The method of claim 3 wherein the degree that SRR and SRL differ from a predetermined threshold is indicated by the color of the bar.
 5. The method of claim 4 wherein a bar is of a first color when the SRR or SRL associated therewith is less than a first preset threshold, a second color when the SRR or SRL associated with that bar is below the first preset threshold and of a third color when the SRR or SRL associated with that bar fall below s a second preset threshold.
 6. The method of claim 1 wherein plungers are affixed to opposed sides of the large diameter piston.
 7. The method of claim 1 and further including the step of providing a pair of hydraulic cylinders each with a relative large diameter piston therein, each having a plunger of a lesser diameter than that of the piston affixed thereto and individually slidable in one of the bores formed in the first and second cylinder blocks.
 8. A monitoring system for indicating operational performance of an intensifier of a water-jet cutting system, the intensifier comprising an inline configuration of at least one hydraulic cylinder containing a piston of a predetermined diameter and having first and second plungers affixed to opposed face surfaces of the piston and cylinder blocks affixed to opposed ends of the hydraulic cylinder and receiving the first and second plungers in cylinder bores formed in the cylinder blocks, the hydraulic cylinder adapted to be coupled to a motor-driven hydraulic pump through a manifold for cyclicly delivering high pressure hydraulic fluid on the opposed face surfaces of the piston characterized in that: (a) first and second end-of-stroke proximity sensors are operatively coupled to the hydraulic cylinder for producing electrical output signals during reciprocal movement of the piston; (b) a microprocessor is provided that receives the electrical output signals and is programmed to measure SRL and SRR values for the first and second plungers; and (c) a graphics display panel is coupled to the microprocessor for graphically indicating when SRL and SRR values approach and decrease below preset thresholds.
 9. The monitoring system of claim 8 wherein the SRL is graphically represented by the size of a first image and SRR is represented by the size of a second image.
 10. The monitoring system of claim 9 wherein the first and second images comprise adjacently positioned rectangular bars whose length dimension are proportional to SRL and SRR values, respectively.
 11. The monitoring system of claim 10 wherein the bars are of a first color when the SRL or SRR associated with the bars are below a first threshold value, a second color when the SRL or SRR associated with the bars decrease below the first threshold, but not a second threshold and a third color when the SRL or SRR associated with the bars decrease below the second threshold. 